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IO20                            Appendix VI.

separate or approach the half-plates. The form of tool for square
holes is given at F, and the corresponding cam on the sleeve at E,
the rotation of E with the plates causing the tool to successively
enter the corners of the dotted square, which is the hole thereby
formed in the work.

P. 775. Further Milling Examples are given in Fig.
932. At A is shewn a 'gang' of milling cutters fixed upon the
milling spindle, by which work of very intricate section may be
very rapidly performed, though considerable driving power is
naturally required. The bolt slots at c and D could scarcely be
tooled with speed and accuracy by any other method than that
of milling, and E shews a use for the face cutter. The plane
table at B is being machined both on top and sides at one cut,
the sides by means of face cutters, and the top by two long
cutters having interrupted teeth, thus giving a clearance for the
shavings which is much needed in roughing cuts. The rig at H
is required when milling a keyway in a round shaft, and consists
of two side clamps, further accuracy of position being secured by
the dummy key in the lower keyway that has already been cut
A twist drill is being formed at G, where the table is swivelled on
its vertical axis to the correct angle, and the drill is rotated in a
bearing at the proper rate of speed to mill the helical groove, the
method being that of screw-cutting with a mill as the tool.

A grooved cam plate of any required design may be milled by
the apparatus shewn at F, which is a plan view. An auxiliary
table a is fixed to the machine table /; and a slide b carries a
spindle k, upon which is the copy c and the work g. When in
operation the weight e pulls the slide b till it rests against the
dummy d fixed on #, and a very slow rotation of the spindle, or
feed, is caused by the worm gear/, separately driven by the cone
pulley k. The result is that the mill/"forms a groove in the work
that is the exact counterpart of the copy c.

Pp. 180 and 811. Milling Machine with Universal
Head.—Fig, 933 shews a large milling machine that may be
easily understood from previous descriptions, The bed A has a
horizontal slide, upon which is the saddle and cross slide M, and
the table B rotated by worm gear N : any desired ratio of feed